Method for making basic furnace bottoms



April 18, 1950 w. s. DEBENHAM 2,504,185

mz'mon FOR MAKING BASIC FURNACE BOTTOMS Filed April 27, 1945 2Sheets-Sheet 1 INVENTOR M44 MMJT DEBENHA/Vl, 91 4, 5

April 18, 1950 w. s. DEBENHAM METHOD FOR MAKING BASIC FURNACE BOTTOMS 2Sheets$heet 2 Filed April 27, 1945 fig.

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Patented Apr. 18, 1950 MAKING BASIC FURNACE BOTTOMS William S. Debenham,

Carnegie-Illinois Stee METHOD FOR tion oi New Jersey Chicago, Ill.,assignor to i Corporation, a corpora- Application April 27, 1945, SerialNo. 590,634

2 Claims. 1

This invention relates to a method of making basic furnace linings andbottoms, and more particularly, the linings and bottoms in furnaces suchas basic open hearth furnaces and electric furnaces with basic linings.

The invention has among its objects an improved method of making basiclinings or bottoms for furnaces whereby such linings or bottoms arecharacterized by being dense, strong, and completely burned. I

This and further objects of the invention will be more readily apparentin th following description.

The method of the present invention is applicable to and displaysadvantages in the making of linings or bottoms in various types offurnaces employing basic materials for such purpose, such as open hearthfurnaces and electric furnaces, where the lining or bottom material isapplied in granular form and is sintered in place. For the purposes ofillustration, however, the invention will be particularly described inconnection with the making of a bottom in a basic open hearth furnacewherein its advantages are particularly great. 7

The invention will be more readily understood by reference to theaccompanying drawings, in which:

Figure 1 is a view in transverse vertical section through a typicalbasic open hearth furnace;

Figure 2 is a view in longitudinal vertical section through a portion ofsuch furnace, said section being taken along the line IIII in Figure 1;

Figure 3 is a view in front elevation of a furnace bottom ramming orpressing device made in accordance with the present invention;

Figure 4 is a view in section through the presser shown in Figur 3, suchsection being taken along the line IV-IV in Figure 3; and

Figure 5 is a view in vertical section through such presser, the sectionbeing taken along the line V-V in Figure 4.

The open hearth furnace 2 which is shown in Figures 1 and 2 provides acovered hearth in the form of a large shallow receptacle in which thecharge of metal is placed, such charge then being subjected to theaction of flames directed over the top thereof alternately from eitherend of the furnace for the purpose of melting the charge to allow itspurification and the addition of desired amounts of alloyingingredients. As a result of the high temperature to which the furnace issubjected, the lining is eroded by the bath, becoming progressivelythinner in successive heats, and therefore frequently must be renewed.

As shown in Figures 1 and 2, furnace 2 is provided with a foundation 4of insulation and/or fireclay brick, a layer of basic brick 6, usuallychrome or chrome-magnesite brick, on top of such foundation, and abottom 8, which, in a basic open hearth furnace, is composed largely ofburned magnesite grain sintered in place on top of the basic brick. Itis with the application of the furnace bottom 8, whether in a newfurnace or in an old furnace upon relining thereof, with which thepresent invention is concerned. Bottom 8 includes beside that part ofthe lining actually in contact with the bath the curved front banks [0shown in Figure 1 leading up to the charging doors I2 of the furnace andthe inclined rearward portion I 4 which is termed the backwall.

Bottoms or hearths of basic open hearth furnaces ar currently preparedby applying high magnesia materials in granular form over a suitablefoundation, such as the layer of brick 6 of the furnace shown, in eitherof the following ways:

1. The material, usually dead burned grain magnesite, is mixed with 10to 25% basic open hearth slag and the mixture is gradually burnedin insuccessive layers approximately one inch thick until the desiredthickness is obtained. As several hours of burning at about 2900 F. istaken for each layer, several days may be required to complete a bottom,but this method produces a well sintered bottom that has fairlysatisfactorily stood the test of time in the industry.

2. The material, size-graded dead burned magnesite or dolomiticmagnesite, to which special air setting bonds including dry sodiumsilicate has been added, is moistened and rammed cold to the desiredthickness with pneumatic hammers, thus producing a dense monolithicbottom, after which the furnace is subjected to heat. This method hasthe advantage of considerable saving in time over the burning-inprocess, and has been largely adopted in recent years. Such rammedbottoms, however, do not sinter completely in service, and while somestrength resides in the unsintered material due to the air settingbonds, these bottoms are frequently friable in the subsurface layers andhave been found often more susceptible to penetration by steel, andconsequently to steel breakouts than the burned-in bottom.

It is the opinion of many that with decreasing steel production rates,the burned-in bottoms will again return to general favor. The burnedinbottoms, however, as made in the prior practice are not ideal since therefractory properties and effectiveness are reduced. by the necessity ofdiluting burned magnesite grains with slag in order to allow the bottomto consolidate and make it dense.- This apparently homogeneous burned-inbottom employing burned magnesite grain and slag is in reality a mixtureof refractory grains in a slag matrix which is quite soft at operatingtemperatures and renders the bottom more susceptible to erosion.Although it is thought by some that the slag has a certain mineralizingeffect on the magnesia grains promoting their growth, it is moregenerally agreed that the higher the MgO content the better the bottom,and thus the slag cannot be considered other than a necessary evil.

The method of the present invention makes possible the use of high MgOcontent grain in the production of a sintered furnace bottom andproduces a dense, strong, completely. burned lining or bottom.Ingeneral, the method consists in pressing the granular material inplace while the furnace is heated, thereby securing the desired degreeof packing of material while the grains are in condition to sinter andbond to each other. The rammer or presser which is the subject ofdivisional application Serial No. 650,176, filed February 26, 1946, nowPatent No. 2,426,673, has proved to be advantageous in carrying out thepresent method. The rammer or presser is inserted within the furnace forsubjecting the bottom to the desired amount of pressure, such presserbeing of such shape as to allow the furnace bottom to be pressed to thedesired contours in different portions thereof.

The presser device consists of a curved form It, preferably made of castiron, such form being roughly of a shape corresponding to half a rightcircular cylinder. One portion of the curved surface thereof, the frontsurface 20, may be made of circular cylindrical contour, but the rearcurved surface 22 thereof, although it may be circular in'crosssectional shape, is preferably made of a longer radius than the frontportion so that it conforms more closely to the surface of the backwallof the furnace. The presser is also provided with two end walls 2| and23 which complete the structure.

presser adaptable to the different contours of the furnace bottom, it isprovided on the front end thereof with three ram engaging sockets 2!,26, and 28 and On the end wall'li with a ram engaging socket 30. Sockets:4, 26, 28 are formed by providing vertical slots in the upper edge ofwall 20 to receive the portion of reduced diameter at the end of thecharging machine ram,

and are completed by a plate 21 welded to the presser having cooperatingrecessed portions and a centrally located hole therethrough for theverticalreception of the flange 29 on the outer end of the chargingmachine ram and the slidable locking pin 3| through ram i5,respectively. Socket It on the end of the presser is similarly 4 formed,with the exceptionthat the plate 32 on the inner surface of the wall 2|contains only one recess for the reception of the flange on the ram.

It will be readily apparent that with the four sockets by which thepresser may be mounted on the ram, the ram, which as is well-known, maybe adjusted angularly in a vertical plane, may be adjustedlongitudinally of the furnace, may be projected into the furnace throughthe charging door to variable extents, and may be rotated about its ownaxis. can present the form to the furnace bottom in such manner that theentire area of the bottom which may be reached through the chargingdoors can be covered and shaped to the desired contour.

In lining a basic open hearth furnace in accordance with the presentinvention, the hearth foundation is prepared in the usual manner and thegrain burned magnesite, which is preferably straight grain burnedmagnesite of fine particle size. containing over MgO is shoveled overthe bottom and burned as in making a regular burned-in bottom. When thebottom has been built up to a depth of approximately six inches and hasattained a surface temperature of approximately 2900 F. or above, thefuel is shut off and the presser member quickly inserted by the chargingmachine through a charging door of the furnace, pushed against thebackwall, dragged across the bottom, rolled against the ends, and pulledagainst the front banks, thereby pressing down the bottom and conformingit to the desired shape. Usually for commercial burned magnesitecontaining 80% Mg() and heated to 2900 F. a pressure of ten pounds persquare inch between the presser and furnace bottom has been foundadequate.

Manipulation of the presser through one furnace door to cover the areaof the furnace bottom which can be reached through that door ordinarilyrequires one or two minutes. Such period of time is insufficient to heatthe presser sufficiently to damage it. The presser is then withdrawn,and the furnace is again heated for onehalf hour to bring the bottomback to temperature, after which the same pressing operation is repeatedfrom the next furnace door and so on until the whole bottom has beenconsolidated in this manner. Usually it is preferred to use two or threesuch complete pressings of the entire furnace bottom area, additionallayers of burned magnesite about four inches thick being shoveled ontothe furnace bottom between successive pressing operations. In someinstances, it is necessary in order to reach areas behind the doorjainbs or to press the curved boundary areas of the furnace bottom, topresent the presser in varying relationships to the furnace bottom. Thiscan be readily done as above described, either by rotating the ram ofthe charging machine, as shown in Figure 2, to make the presser conformto the area engaged or in some cases to withdraw the presser from thefurnace, place it on a suitable support and to engage it at a differentsocket by the charging machine ram. Such operation may be quickly andeasily accomplished and does not need entail undue cooling of thefurnacebottom. Although the presser has been described as merely being draggedover the furnace bottom, the charging machine upon which it is mountedmakes possible, if desired,

, a tamping action by raising and lowering the MgO grain. it is obviousthat the invention displays advantages when small amounts of fluxes, forexample, up to 5% flux, are incorporated therein.

It is obvious that variations are possible in the method disclosed, andit is to be understood, therefore, that the scope of the invention isnot limited to the disclosed embodiments thereof but is defined by thefollowing claims.

Iclaim:

1. The method of making bottom in a basic furnace which comprisesapplying a layer of granular basic refractory material high in MgO tothe inner bottom refractory surface of the furnace, heating the layer ofmaterial throughout to a sintering temperature, and subjecting theheated layer to pressure to compact the layer and shape it to thedesired contour, said pressing operation being effected in successivelocalized areas by subjecting the layer in such areas to a pressure onthe order of 10 lbs/in. in a direction generally downwardly against thelayer of refractory thereunder.

2. The method of making bottom in a basic open hearth furnace whichcomprises applying a layer of granular basic refractory materialcomposed substantially wholly of straight grain burned magnesite to theinner bottom refractory surface of the furnace, heating the layer ofmagnesite throughout to approximately 2900 F., and &

subjecting the heated layer to pressure applied to the top of the layerin a direction generally REFERENCES CITED The following references areof record in the file of this patent:

UNITED STATES PATENTS

